Along with the constant evolution of a wireless communication technology and protocol standard, a mobile packet service has experienced great development, and a data throughput capability of a single terminal has been continuously improved. For example, a Long Term Evolution (LTE) system may support data transmission at a maximum downlink rate of 100 Mbps within a 20 M bandwidth, and a data transmission rate of a follow-up LTE Advanced (LTE-A) system may further be increased, and may even reach 1 Gbps.
Inflationary increase of a data service volume of a terminal imposes enormous pressure and challenges for a service capability and deployment strategy of the terminal. An operating company needs to enhance an existing network deployment and communication technology on one hand, and on the other hand, expects to accelerate the popularization of a new technology and network extension, thereby fulfilling the aim of rapidly improving network performance. Along with the development of a mobile communication system up to now, it is more and more difficult to provide economic, flexible and high-capability service only by enhancing macro networks, so that a network strategy of deploying Low Power Nodes (LPN) to provide a small cell coverage becomes an attractive solution, particularly in the aspect of providing good user experiences for a user in an indoor/outdoor hotspot area with a large transmitted data volume.
Enhancement in small cell deployment has been confirmed by the Third Generation Partnership Project (3GPP) to be one of the most interesting issues in future network development. Small cells are deployed in a coverage of a macro network, which may make transmission, mobility, security, interference and the like greatly different from those of a conventional macro network, and in a process of independently providing service for a terminal by each Evolved Universal Terrestrial Radio Access Network NodeB (eNB), there may exist multiple problems, and service requirements on large data volume and high mobility cannot be met; and because of practical limitations, historical factors and the like, backhauls of an LPN are diversified, and each interface has different characteristics, and is limited to coordinate and interact with the macro network. Therefore, in a scenario deployed with small cells, how to maintain a good coordination mechanism with a Macro eNB (MeNB) by virtue of its characteristics to provide optimal communication service for User Equipment (UE) to further meet requirements of higher bandwidth, higher performance, lower cost, higher security and applicability to multiple backhauls is an important topic urgent to be solved in the future development of an LTE communication system.
The deployment of a large number of small cells also brings many new problems, for example, the deployment of the small cells may cause frequent mobile processes of a terminal between the small cells and macro cells and between the small cells. Frequent Handover (HO) may cause higher signalling impact between a Core Network (CN) and an eNB, and meanwhile, frequent HO may also cause frequent interruption of a service and increase the probability of call drop of the terminal.
FIG. 1 is a topology diagram of a typical LTE/LTE-A network according to a related technology. As shown in FIG. 1, UE moves around cell 1-1 (Cell1-1), cell 2-1 (Cell2-1), cell 2-2 (Cell2-2) and cell 3-1 (Cell3-1), eNBs are network control nodes of cells, one eNB may control one or more cells, and as shown in FIG. 1, Cell1-1 is controlled by eNB1, Cell2-1 and Cell2-2 are controlled by eNB2, and Cell3-1 is controlled by eNB3. The eNBs are connected through X2 interfaces, and each eNB is connected with a CN through an S1 interface.
FIG. 2 is a flowchart of X2 HO of LTE according to the related technology, and as shown in FIG. 2, the flow includes the following steps:
Step 202: UE sends a measurement report to a source eNB.
Step 204: an HO decision is made.
The HO decision is made by the source eNB. A making basis may be the measurement port sent by the UE, or some own measurement information or local load information of the source eNB, so when to initiate HO is determined according to own algorithm of an implementer. After HO is determined to be initiated, Step 206 is executed.
Step 206: the source eNB sends an HO request to a target eNB.
Once it is determined that cross-eNB HO is required, an eNB where a target cell is located is the target eNB, and because the target eNB does not have context information of the UE, the source eNB sends necessary configuration information of the UE on the source eNB to the target eNB by sending the HO request to the target eNB. Wherein, the HO request includes the context information of the UE and Radio Resource Control (RRC) context information. The context information of the UE may include information such as a corresponding identifier of X2/S1 of the UE, a context (including address information of a ground transmission network, Quality of Service (QoS) and the like) of an E-UTRAN Radio Access Bearer (E-RAB), security-related information and terminal capability. An RRC context is a radio resource configuration of a cell where the UE is located, and includes information such as a Cell Radio Network Temporary Identifier (C-RNTI) of the UE, an access layer configuration, a physical cell ID and a short Message Authentication Code-Integrity (MAC-I) for RRC reconfiguration.
Step 208: admission control is performed.
The target eNB configures new context information according to the context information of the source eNB and a resource state of the target eNB, and modifies the RRC configuration of the UE according to a local radio resource condition if necessary, for example, modifies a new physical cell ID, a new C-RNTI, a random access dedicated resource, broadcast information of a new cell, updated security information and the like.
Step 210: HO request Acknowledgement (Ack) is sent.
The target eNB generates RRC Reconfiguration (Reconfig) according to the modified configuration, and sends RRC Reconfig to the source eNB through HO request Ack.
Step 212: RRC Reconfig is forwarded.
The source eNB receives RRC Reconfig from the target eNB, performs integrity protection and encryption processing on RRC Reconfig, and sends RRC Reconfig to the UE.
Step 214: the UE performs random access.
The UE performs random access in the target cell after receiving RRC Reconfig.
Step 216: the UE sends RRC Conn.Reconf.Complete.
The UE returns RRC Conn.Reconf.Complete to the target cell after successfully performing random access in the target cell.
Step 218: the target eNB sends a path switch request.
The target eNB then sends the path switch request to a Mobile Management Entity (MME).
Step 220: the MME sends a modify bearer request to a serving gateway.
Step 222: the serving gateway switches a Downlink (DL) path.
The serving gateway modifies a data path of the CN from the source eNB to the target eNB.
Step 224: the serving gateway sends a modify bearer response.
Step 226: the MME returns a path request Ack to the target eNB.
Step 228: the target eNB sends a UE context release message to the source eNB.
Step 230: the source eNB releases a resource.
The source eNB releases a context of the UE and a related dedicated resource.
From the above flow of HO of the LTE system, the whole HO is a serial process, that is, it is necessary to determine the target eNB at first, then the source eNB and the target eNB finish the context preparation of the UE, next the UE finishes the access of the target eNB, and finally the CN performs path HO. By characteristics of such a serial process, a failure of any intermediate step may cause a failure of the whole flow, a time delay of any step may cause a time delay of the whole system, and it is necessary to execute the whole flow during every HO even if it is back and forth HO between the same two cells.
When a large number of small cells are deployed, for the problem of high HO failure rate during HO in the related technology, there is yet no effective solution.